Method for producing cartridge heaters

ABSTRACT

A method for producing cartridge heaters in which a going and returning heating coil is inserted into a heat-resisting cover pipe with an elliptical cross-section so as to align the crosssections of the going and the returning portions of the heating coil along the longer axis of the elliptical cross-section of the cover pipe, powdered insulator is charged in the space within the cover pipe not occupied by said coil, the longer axis is reduced by compressing the cover pipe in the direction along the longer axis and the cross-section of the heating coil is deformed into an ellipse having its longer axis perpendicular to the direction of the compression.

United States Patent [191 Saku [ Dec. 30, 1975 [54] METHOD FOR PRODUCING CARTRIDGE HEATERS [75] Inventor:

[73] Assignee: Kabushikikaisha Kawaidenkiseisakusho, Nagoya, Japan 22 Filed: July 12,1974

211 Appl. No.: 487,958

Isamu Saku, Aichi, Japan [30] Foreign Application Priority Data FOREIGN PATENT S OR APPLICATIONS 717,494 10/1954 United Kingdom 29/614 Primary Examiner-Victor A. Di Palma Attorney, Agent, or FirmWilliam Anthony Drucker [57] ABSTRACT A method for producing cartridge heaters in which a going and returning heating coil is inserted into a heatresisting cove-r pipe with an elliptical cross-section so as to align the cross-sections of the going and the returning portions of the heating coil along the longer axis of the elliptical cross-section of the cover pipe,

powdered insulator is charged in the space within the p cover pipe not occupied by said coil, the longer axis is reduced by compressing the cover pipe in the direction along the longer axis and the cross-section of the heating coil is deformed into an ellipse having its longer axis perpendicular to the direction of the compression.

3 Claims, 7 Drawing Figures US. Patent Dec. 30, 1975 METHOD FOR PRODUCING CARTRIDGE HEATERS BACKGROUND OF THE INVENTION This invention relates to a method for producing cartridge heaters having a cover pipe and a going and returning heating coil contained therein. This kind of cartridge heater comprises a heat-resisting cover pipe a going and returning heating coil 11 contained therein and powdered insulator 12 charged in the space within the cover pipe not occupied by the heating coil. As insulation must be maintained between the heating coil and the cover pipe and between the going and the returning portions of the heating coil, the circular cross-sectional area of the heating coil is limitted to within a certain value when the diameter of the cover pipe is kept constant. For this reason, the length of the resistance wire of the heating coil containable in unit length of the cover pipe is limitted and the heat generated in unit length of the heating coil is subject to limitation. When the density of the heat generated must be large, it can not be avoided to use a heater under an over-load condition by passing an over-current in the resistance wire. It can be considered to make the crosssection of the heating coil elliptical in order to increase the quantity of the resistance wire containable in unit length of the cover pipe. However, it is not easy to make the cross-section of the heating coil elliptical and such heating coil is apt to be damaged in a manufacturing process.

The powdered insulator is charged within the cover pipe during a process where only a guiding jig is pulled out from the cover pipe after the heating coil held firmly by the guiding jig has been inserted in the cover pipe as shown in FIG. 5. In this charging process, some oscillation is applied to the cover pipe longitudinally and transversely in order to enlarge the charging efficiency and so it happens that the circular cover pipe is rotated against the heating coil, the heating coil being twisted. This twist of the heating coil is apt to occur more often when longer heaters are manufactured. If the heating coil is provided with some clamp in order to eliminate this twist, the oscillation for effectuating the charging of the powdered insulator is weakened and the charging work becomes troublesome.

SUMMARY OF THE INVENTION A going and returning heating coil is inserted in a cover pipe having an elliptical cross-section and the cross-sections of the going and the returning parts of the heating coil are aligned on the longer axis of the ellipse. This arrangement of the cover pipe and the heating coil itself makes the going and the returning portions of the heating coil difficult to be twisted and moreover, the prevention of the twist is still effective, if a guiding jig fit in the cover pipe for inserting the heating coil is used. After the powdered insulator has been charged within the cover pipe, the cover pipe is compressed along the longer axis of it and the cross-section of the cover pipe is deformed to be substantially circular in most cases, that of the heating coil becoming elliptical at the same time. When the cross-section of the compressed cartridge heater is observed, it is found that the cross-sectional area of the heating coil deforms elliptically and extends in such a region in the cover pipe that was not made use of in a conventional cartridge heater where a going and returning heating coil with a circular cross-section is contained within a cover pipe with a circular cross-section. The density of heat generated in unit length of a heater is much increased.

The salient relationships of the present invention have been made clear and it will be understood that the heater according to the present invention is easy to manufacture and of high heat-generating density. The other objects of the present invention will become clear in conjunction with the following detailed description and drawings.

IN THE DRAWINGS FIG. 1 is a cross-sectional view of a cartridge heater according to the present invention before it is compressed.

FIG. 2 is a cross-sectional view of the heater in FIG. 1 after it is compressed.

FIG. 3 is a cross-sectional view of a conventional heater before it is compressed.

FIG. 4 is a cross-sectional view of the heater in FIG. 3 after it is compressed.

FIG. 5 is a front elevational view of partial section showing the cartridge heater according to the present invention in a powdered insulator charging process.

FIG. 6 is a section taken on a line 66 of FIG. 5.

FIG. 7 is a longitudinal section for showing the situation of a heating coil.

Referring to the drawings, 10 shows generally a cover pipe having an elliptical cross-section and made of heat-resisting material such as stainless steel or copper. A heating coil 11 is made of a resistance wire wound helically and has a circular cross-section. Either end of the heating coil is connected to a lead wire 14 by means of a terminal pin 13 and hook 13a. A guiding jig or a guiding pipe 15 for inserting said heating coil into the cover pipe 10 has an elliptical cross-section similar to and smaller than that of the cover pipe in order to be inserted in the cover pipe 10 and is provided with a pair of guiding paths 16 having a cross-section suitable for passing the heating coil 11 therein. Said heating coil 11 is bent at the middle portion and passed through the pair of guiding paths. Next the guidingjig 15 containing the going and returning heating coil 11 therein is inserted in the cover pipe 10. The cross-sections of the going and the returning portions of the heating coil 11 are aligned within the cover pipe 10 along the longer axis of its elliptical cross-section. While only the guiding jig 15 is pulled out from the cover pipe 10 and longitudinal and transverse oscillations are applied to the cover pipe, some powdered insulator 12 such as alumina or magnesia is charged on. The relative rotation between the cover pipe 10 and the guiding jig resulting from the oscillation for increasing the charging efficiency of this powdered insulator I2 is prevented in this case because the cross-section of them are nested ellipses. After the charging of the powdered insulator is finished, the cover pipe 10 is compressed by a diameter-reducing machine such as a awaging machine or a roll-press along its longer axis indicated by an arrow 17. Also in the direction along the shorter axis shown by an arrow 18, the cover pipe is compressed to some extent in order to prevent the cover pipe from extending in this direction and to effectuate more or less compression. As the result of compression, the powdered insulator 12 becomes of high density and on the other hand the cross-section of the cover pipe deforms to be substantially circular and the cross-section of the heating coil becomes an ellipse having its shorter axis along the direction of the compression, that is, the direction of the longer axis of the cross-section of the cover pipe before compression. By comparing FIGS. 2 and 4, it is easily found that the elliptically deformed heating coil 11 is extending into the region, where a heating coil 11' would not be situated in a conventional cartridge heater, without reducing the insulating distance between the cover pipe and the heating coil 11 and between the going and the returning portions of the heating coil. Thus, the quantity of resistance wire containable in unit length of the heater is increased and thereby heat generated in unit length of the heater is also enlarged.

What I claim is:

l. A method for producing cartridge heaters, which includes the steps of inserting a going and returning heating coil of a circular cross-section within a heatresisting cover pipe with an elliptical cross-section, the

heating coil being aligned along the longer axis of the elliptical cross-section of said cover pipe, charging powdered insulator in the region within the cover pipe not occupied by said heating coil and reducing said longer axis by compressing said cover pipe along said longer axis to deform the cross-section into a less eccentric ellipse and the cross-section of said heating coil into an elliptical one having its longer axis perpendicular to the direction of compression.

2. A method for producing cartridge heaters according to claim 1 including the step of using a guiding jig having a cross-section suitable for being set within the cover pipe before compression and provided with a pair of parallel guiding paths for inserting said going and returning coil in said cover pipe.

3. A method for producing cartridge heaters according to claim 1 including the step of making the crosssection of said cover pipe circular by compressing said 

1. A method for producing cartridge heaters, which includes the steps of inserting a going and returning heating coil of a circular cross-section within a heat-resisting cover pipe with an elliptical cross-section, the cross-section of the going and returning portions of the heating coil being aligned along the longer axis of the elliptical cross-section of said cover pipe, charging powdered insulator in the region within the cover pipe not occupied by said heating coil and reducing said longer axis by compressing said cover pipe along said longer axis to deform the cross-section into a less eccentric ellipse and the crosssection of said heating coil into an elliptical one having its longer axis perpendicular to the direction of compression.
 2. A method for producing cartridge heaters according to claim 1 including the step of using a guiding jig having a cross-section suitable for being set within the cover pipe before compression and provided with a pair of parallel guiding paths for inserting said going and returning coil in said cover pipe.
 3. A method for producing cartridge heaters according to claim 1 including the step of making the cross-section of said cover pipe circular by compressing said cover pipe. 